This invention relates generally to materials separating apparatus and is concerned more particularly with separating apparatus having means for segregating nonferromagnetic metals from commingled materials.
Solid municipal waste may be shredded and then classified into light and heavy fractions, each having therein items suitable for recycling. The light fraction, for example, usually includes paper and cardboard which may be used in the production of new paper products or may be sold as combustible fuel. The heavy fraction generally is comprised of glass, ceramic, wood, ferromagnetic materials, and nonferromagnetic metals, for examples. The ferromagnetic materials may be extracted by conventional means, such as electromagnets, for example, and used in the manufacture of steel and other metal alloys.
The heavy fraction of municipal waste also includes at least two other categories of potentially saleable items, namely nonferromagnetic metals and clean glass. The nonferromagnetic component of the heavy fraction generally is comprised of aluminum scrap, copper-zinc base scrap, and tin scrap, for examples. Market analysis indicates that there is a greater demand for the nonferromagnetic metals than for other components of the heavy fraction. Thus, although constituting only about one percent by weight of typical municipal waste, the nonferromagnetic metals nevertheless represent a significant percentage of the total resale value.
Accordingly, prior art means have been developed for separating nonferromagnetic metals from other components of municipal waste. These prior art means generally involve heavy media separation, electrostatic separation, or electromagnetic separation. However, heavy media separation has not been generally satisfactory due to fluids becoming entrapped in the crushed items of municipal waste and erratically affecting their specific gravities. Electrostatic separation generally requires the use of complicated apparatus for establishing a strong electrostatic field which induces electrostatic charges on respective items of municipal waste. Electromagnetic separation generally involves the use of sophisticated electrical equipment and circuitry for producing a time varying electromagnetic field which induces eddycurrents in the nonferromagnetic metal objects in municipal waste.
Therefore, it is advantageous and desirable to provide materials separating apparatus with simple and relatively inexpensive means for segregating the nonferromagnetic metal items in commingled waste materials.